1. Field of the Invention
The present invention relates to a plate-like multiple antenna composed of a conductor plate, which is compact and low-profile, besides, which may be easily housed in electric equipment such as personal digital assistance, and electrical appliances as well as in walls and the like; and the electrical equipment provided with such multiple antenna.
2. Prior Art
In recent years, downsizing for a variety of antennas for exclusive use in equipment including personal digital assistance, mobile computers, and the like (hereinafter referred simply to as “personal digital assistance” in a lump) except for large antennas for base station and satellite broadcasting has been actively made. Particularly, an antenna for personal digital assistance required for downsizing involves a problem of a space for installing the antenna, and a problem of a demand for performance acting counter to restriction in an antenna volume with downsizing of the personal digital assistance itself.
Furthermore, the same problem arises in a dimension of antenna itself with introduction of an antenna inside a wall in a room or introduction of such antenna into personal computer, electric appliances (hereinafter referred simply to “electric appliance” in a lump) or the like in a wireless network concept in home, which has been actively studied recently.
The above-described problem is due to such a cause that an exclusive space must be separately maintained in the case where an exclusive antenna is to be housed in a cabinet or a main body casing (hereinafter referred simply to as “cabinet” in a lump) in personal digital assistance or electric appliances. Moreover, with downsizing and weight reduction of products, an antenna itself is naturally required for downsizing and weight reduction thereof, so that it is difficult to satisfy required performance of the antenna.
Namely, it is necessary for maintaining a certain space for installing an antenna inside a cabinet for housing the antenna into the cabinet and maintaining its performance. As a result, there arises increase in manufactures' costs of the resulting products, and prolongation of a term for development, because of alteration of respective specifications, which have been heretofore employed.
In order to avoid these problems, substantially all of personal digital assistances or electric appliances use a separate cabinet outside the main body cabinet and to which an external antenna is attached by a separate cable.
In this manner, however, there are many cases wherein an external antenna must be once removed in the case when the personal digital assistances or electric appliances are transferred. In addition, troubles for reinstallation or readjustment of the antenna occur, there arises antenna damage due to routing of cables or the like, or unexpected troubles according to circumstances. Besides, a degree of freedom relating to a position for installing personal digital assistances or electric appliances is restricted. Thus, a user has been always accompanied with such troubles as described above.
For eliminating the problems as described above, there are typical well-known examples of a low-profile antenna, which can be housed in a clearance or the like inside a personal digital assistance or a cabinet of electric appliances, disclosed in Japanese Patent Laid-Open Nos. H5-22018 and H8-256009.
These well-known antennas are low-profile types, respectively, and they are easily manufactured. However, a constitution of these well-known antennas requires a wide ground section for obtaining high radiation gain by means of these antennas, so that the resulting product has a tendency of having a larger structure.
For this reason, in order to assure high radiation gain and to make the structure smaller, an earthing section (ground) or an earthing conductor (ground) of a high-frequency circuit in an equipment cabinet is connected directly with a ground section of an antenna in accordance with a high-frequency manner by means of metallic screws, welding or the like, whereby a distribution of electric current on the antenna is allowed to exist on the conductor part also, and finally the ground inside the equipment cabinet must be utilized as a part of ground section of the antenna.
In other words, it is required in the well-known examples that an antenna's ground section is connected directly with ground in a cabinet by means of metallic screws, welding or the like at a position or in a part of space where the antenna is to be installed, and as a result, these well-known antennas are not suitable for a demand of downsizing and weight reduction, so that these well-known antennas exhibit poor multiusability.
On one hand, a consumptive demand for such type of personal digital appliances that a plurality of wireless communication systems using radio waves of different frequency bands can be utilized by a single personal digital appliance are increasingly developing lately. Such demands are derived from countermeasures for a novel communication system aiming at speedup in communication speed, a tendency of high capacity of information, and adequate and differential services, or countermeasures for diversification in personal digital appliances, and a transitional period from an existing system to a novel communication system.
In these circumstances, if individual antennas are provided, respectively, for a plurality of frequencies to be used in a single personal digital appliance, it makes to be worse the above-mentioned problems. Thus, it is required that radio waves in a plurality of frequency bands can be transmitted and received by a single antenna.
As is apparent from the above description, respective exclusive antennas to be housed in personal digital appliances or home electric appliances for a wireless network in home must not bring increase in manufactures' costs of the resulting products, prolongation of a term for development and the like, but they can be easily introduced, and they can reduce users' troubles.
Furthermore, it is required that an antenna itself is inexpensive.
Moreover, it is necessary for realizing a multiple antenna by which radio waves in a plurality of frequency bands can be transmitted and received by a single antenna as countermeasures for diversification in personal digital appliances, and a plurality of communication systems.